Large-scale and Convective-scale Updraft Profiles from Satellite Observations

Abstract:

Among the crucial problems involved in the tropical energy budget are the thermodynamic effects of an ensemble of convective clouds on their environment and the large-scale influence imposed back on the convective-scale dynamics. Efforts to seek observational evidence for this problem, however, are challenged by limitations in the capability of measuring vertical motion across different horizontal scales. We have recently been exploring new analysis strategies in hopes to make this seemingly impossible possible, exploiting a suite of satellite instruments including the CloudSat and TRMM radars and Aqua AIRS.

Since a complete vertical structure of in-cloud vertical velocity, w_c, is unable to be reconstructed from satellite measurements alone, a single-column plume model is run with the environmental soundings from AIRS to obtain a set of synthetic w_c profiles under a range of entrainment rates. The solutions are then narrowed down in a Bayesian manner so as to match the cloud-top vertical velocity and buoyancy estimates from A-Train infrared and radar measurements. The vertical profile of large-scale mean vertical motion, ω, is also evaluated from satellite observations in its own approach: ω as a function of pressure is determined so that it satisfies the horizontal divergence terms in the tropospheric water and thermal budget equations in which the remaining terms are constrained by satellite measurements.

In this talk, the methodology is briefly outlined and the results are presented and discussed in light of outstanding issues in tropical dynamics. The w_c and ω estimates above, although subject to intrinsic uncertainties yet to be verified, do not involve any closure assumption as required for cumulus parameterizations and would offer a useful test bed for climate models and reanalysis data as well as a unique opportunity to study the mechanism of tropical convection.